I mean that there could be a situation like in Bitcoin today - in the case Ardor gets popular -, that many transactions are waiting in the mempool to be confirmed. I don't know if there is a block size limit / transaction number limit for child chain blocks, but I think I remember that in NXT there was such a limitation (for regular blocks).

In this case, a pegged childchain like the "IgnisPeg" I describe in the other post could relieve the block size problem. Also if the Ignis childchain gets very big (I know it's prunable, but the community should aim for a large number of full archival nodes) it would make sense, even if there was no bottleneck with transactions.

I've dived a bit in the NXT documents and there seems to be a mechanism for such "pegged coins": a combination of the "Claimable" and the "Reservable" properties of a MS currency. My question is, then: Would this be also possible in Ardor with child-chain currencies (the peg could be with ARDR or with IGNIS or another childchain)?

(I know it's a long-term problem, but as Ardor is specially built with scalability in mind, it would be a very nice feature).